Valorization of Lemon Processing By-Products Through Multi-Strain Fermentation: Strain-Specific Changes in Flavonoids, Limonoids, and Antioxidant Capacity

Lemon processing by-products are rich in flavonoids, limonoids, and phenolic acids, but their direct utilization is limited by glycoside-dominant flavonoid profiles, bitterness-associated limonoids, and insufficiently defined valorization strategies. This study compared eight food-relevant microorganisms, including lactic acid bacteria, Bacillus, yeast, and filamentous fungi, using a common aerobic submerged fermentation framework for lemon by-products. Rather than evaluating fermentation as a single uniform process, the study aimed to determine whether different microbial groups could redirect the same substrate toward distinct functional remodeling profiles. Targeted HPLC analysis of flavonoids, limonoids, and phenolic acids, together with DPPH and ABTS radical-scavenging assays, revealed clear strain-dependent differences in metabolite remodeling and antioxidant outcomes. L. plantarum showed the most consistent antioxidant enhancement profile, characterized by increased hesperetin and phenolic acid responses together with low DPPH and ABTS IC50 values. L. pentosus promoted flavonoid remodeling but showed a more timing-sensitive antioxidant response. S. cerevisiae tended to preserve glycosylated flavonoids and showed a release-oriented phenolic acid profile with strong early ABTS activity. R. stolonifer exhibited the most pronounced limonoid remodeling, including marked limonin reduction and obacunone accumulation, suggesting potential relevance for bitterness-oriented applications. These findings demonstrate that different microorganisms can be functionally classified according to their dominant remodeling tendencies, including antioxidant enhancement, flavonoid conversion, glycosylated flavonoid preservation, phenolic acid release, and limonoid-associated debittering. This functional classification provides a practical basis for selecting microorganisms according to the intended application of lemon by-product valorization.